Spectrum allocation and/or management in a shared spectrum environment is sometimes controlled by a central management/allocation engine as part of a “top down” spectrum allocation approach. The engine identifies channels that are not occupied by an incumbent radio in the location of a device requesting spectrum and deems those channels available for use by the requesting device. Exemplary channels that may be allocated in this manner are TV white spaces. The knowledge of the incumbent radio devices is obtained from a database that contains information regarding incumbent users and a protected area for each incumbent user. The protected area for each incumbent may be determined by regulation or by calculation using the location of the incumbent device's transmitter and transmission characteristics (e.g., antenna height, transmit power, etc.). This type of spectrum management relies on prior (a priori) knowledge of information relating to the incumbent users.
Another approach to gaining access to spectrum in a shared environment involves use of spectrum sensing in a “bottom up” spectrum allocation approach. In this approach, a cognitive radio senses its surrounding spectrum environment and avoids channels on which the cognitive radio senses the presence of an incumbent user.
Each of these approaches has limitations in its effectiveness in certain situations. For example, there are some incumbent radios that may move or may not always be active. Therefore, there are times when a secondary user may be able to use the spectrum ordinarily used by the incumbent radio. But a top-down approach is difficult to apply due to the unpredictable spectrum use made by the incumbent user. Also, applying policies regarding spectrum use in a bottom up approach is not practical.